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Here are the most informative how-to articles on this site:
LiPo Voltages
Here’s a handy chart to help you estimate remaining capacity in a LiPo battery. When you’re flying a new plane, fly it for a 2 minutes at normal throttle, let the battery rest for 2 minutes, then check the battery voltage. If your battery is at 60% capacity, for instance, you can fly for about 6 minutes. (Usual disclaimers apply: this is only an estimate.)
View a printable PDF version of this chart. Download the Excel spreadsheet.
Time your flights and respect your batteries! I don’t let my batteries get below 3.7 volts per cell, and I’m able to keep using them for more than two years of frequent flying. I also never experience Low Voltage Cutoff from my speed control, which eliminates unplanned landings.
How Many Watts?
How much power do you need for that model you’re building? For electric flyers, plan on at least 50 watts per pound to take off and fly. You’ll want 100 watts per pound for acrobatic performance and at least 150 watts per pound for extreme challenges such as 3D flying.
Watts (P) are the result of current (I) times voltage (E): P = I * E (P stands for power, obviously; less obviously, E stands for Electromotive force [voltage] and I don’t know what I stands for, but it’s current).
Since I have trouble thinking in terms of watts, I’ll often redefine power requirements in terms of amps. I’ll assume a 3S LiPo, 12.6 volts at full charge, and round it down to 10 volts for easy and conservative calculation, then figure out my amp needs.
Restated this way, I want 10 amps per pound for acrobatic performance and 15 amps for dramatic flying. If a 1320mAh 3S battery is rated at 15C, it can theoretically deliver a current of 1.32 * 15 = 19.8 amps, which means that I could use it to fly at 2-pound plane with acrobatic results.
